In shearing of plates or sheers the quality of cutting depends on the clearance between the blades, which should be proportional to the thickness of the material being cut, and on the proportionality ranging from 30 to 50 percent of the clamping force acting on the plate under shearing to the shearing force. in addition, the quality of shearing is dependent on the nature of motion, rectilinear or curvilinear, of a movable blade. Preference is given to the rectilinear motion of the movable blade, since it prevents the non-working surface thereof from running against the cutting edge of the fixed blade. In this way it becomes possible to maintain an adequate clearance between the blades throughout the operating cycle.
There ae known shears for plates or sheets (Germany, Federal Republic of, Pat. No. 1,502,879 cl. 31/04, 1970, issued on July 22, 1971, Applicant Maschinenfabric Sack G.m.b.H.), which comprise a bed-mounted fixed blade co-operating with a movable blade rigidly secured on a beam. Mounted in the guides of the bed is a clamping beam pivotally connected to a two-arm lever which, in turn, is articulated to the bed so that one of its arms is connected to the bed through the agency of a hydraulic cylinder and carries a roller interacting with a driven cam, the other arm of the lever co-operating with the clamping beam. Mounted in the clamping beam is a blade beam which is connected to a drive. Though in these shears the inter-blade clearance is set automatically in accordance with the thickness of the material, yet they fail to ensure proportionality in the clamping force acting on the plate or sheet to the shearing force. Moreover, the provision of individual drives for actuating the clamping and blade beams renders there shears more complicated in construction.
There are also known plate shears which comprise a bed-mounted fixed blade co-operating with a movable blade rigidly fixed on a blade beam mounted in clamping beam articulated to the bed, and a drive for actuating the clamping and blade beams. The clamping beam is pivotally connected to the bed with the possibility for turning motion enabling contact with the surface of a sheet or plate subjected to shearing. The beam with the movable blade fixed thereon is pivotally connected to the clamping beam and articulated directly to the drive. The articulations and the pivot are mutually arranged so as to ensure proportionality of the material resistance to shearing. An adequate clearance between the blades in these shears is set automatically in proportion to the thickness of the material being cut, and the power-driven blade beam gives up to the clamping beam the clamping force acting on the plate or sheet, which is proportional to the shearing force. its value is determined on account of the relationship between the application of the arms of force and the reaction to the axis of oscillation of the clamping beam. However, the shears described above permit quality shearing of sheets having only 4 mm in thickness and 3000 mm in width. The shearing of plates with a width of more than 3000 mm is pratically impossible, since during the turning motion of the clamping beam, the non-working surface of the movable blade is run against the cutting edge of the fixed blade and thus precludes the possiblity of maintaining on adequate clearance between the blades in the course of shearing. The under-blade bed at the blade beam, performing turning motion during shearing, is made to conform in shape to quadratic curve, and the blade is mounted on the beam so that when in fixed position its cutting edge also acquires the form of quadratic curve. Treating of such a bed and a long blade is technologically inefficent and requires special equipment.